In hydraulic systems for moving loads such as an excavator boom it is common to utilize two actuators such as cylinders to move a single load. In such systems where there are individual valves controlling each cylinder, there is a tendency for one cylinder to provide the entire lifting force because of the difficulty in controlling the flow to each actuator.
Accordingly, an objective of the present invention is to provide a system wherein the pressures are equalized when two actuators are supplied from a pump. It is a further objective to provide such a system for use in a system shown and claimed in U.S. application Ser. No. 024,058 filed Mar. 26, 1979, now U.S. Pat. No. 4,201,052, having a common assignee with the present application, wherein pilot operated meter-in valves are used to control flow to the cylinders. In such a system, the characteristics of the meter-in are not matched perfectly. Further, if the meter-in valves are pressure compensated, there is a tendency for one cylinder to carry all of the load, and the other to have a high differential pressure drop across the meter-in valve.
In accordance with the invention the load on each actuator cylinder is sensed and the average is applied to the load responsive means for varying the displacement of a variable displacement pump.